Copy-protected optical media and method of manufacture thereof

ABSTRACT

A computer-readable medium having material at a select position therein and containing instructions for controlling an optical reader to cause the optical reader to re-read the position having the material one or more times to elicit a measurable parameter at such position.

RELATED ART

This application is a continuation application of U.S. patentapplication Ser. No. 09/879,457, filed on Jun. 12, 2001, now U.S. Pat.No. 6,638,593, which is a continuation-in-part of U.S. patentapplication Ser. No. 09/821,577, filed on Mar. 29, 2001, now U.S. Pat.No. 6,589,626, which is a continuation-in-part of U.S. patentapplication Ser. No. 09/739,090, filed Dec. 15, 2000, now abandoned,which is a continuation-in-part application of U.S. patent applicationSer. No. 09/631,585, filed Aug. 3, 2000 and U.S. patent application Ser.No. 09/608,886, filed Jun. 30, 2000, from which priority is claimed, allof which are herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to copy-protected opticalinformation recording media and methods for manufacturing the same. Morespecifically, the present invention relates to the manufacture of anoptically readable digital storage medium that protects the informationstored thereon from being copied using conventional optical mediumreaders, such as CD and DVD laser readers, but permits reading of theinformation from the digital storage media by the same readers.

2. Background of the Invention

Optical data storage media (“optical media”) are media in which data isstored in an optically readable manner. Data on optical media areencoded by optical changes in one or more layers of the media. Opticaldata media are used to distribute, store and access large volumes ofdata. Formats of optical medium include read-only formats such as CD-DA(digital audio compact disc), CD-ROM (CD-read-only memory), DVD (digitalversatile disc or digital video disc) media, write-once read-many times(WORM) formats such as CD-R (CD-recordable), and DVD-R (DVD-recordable),as well as rewritable formats such as found on magneto-optical (MO)discs, CD-RW (CD-rewritable), DVD-RAM (DVD-Random Access Media), DVD−RWor DVD+RW (DVD-rewritable), PD (Phase change Dual disk by Panasonic) andother phase change optical discs. Erasable, or rewritable, optical discsfunction in a similar manner to magneto-optical (MO) disks and can berewritten over and over. MO discs are very robust and are geared tobusiness applications, typically in high-capacity disk libraries.

Optical media have grown tremendously in popularity since their firstintroduction owing in a great deal to their high capacity for storingdata as well as their open standards. For example, a commerciallyavailable magnetic floppy diskette is only capable of storing 1.44 Mb ofdata, whereas an optical CD-ROM of approximately the same size can havea capacity in excess of 600 MB. A DVD has a recording density which issignificantly greater than a CD. For example, conventional DVD read-onlydiscs currently have a capacity of from 4.7 GB (DVD-5, 1 side/1 layer)to 17.0 GB (DVD-18, 2 sides/2 layers), write-once DVDs a capacity of3.95 GB (DVD-R, 1 side/1 layer) to 7.90 GB (DVD-R, 2 sides/1 layer)(newer DVD-Rs can hold up to 4.7 GB per side), and conventionalrewritable DVDs of from 2.6 GB (DVD-RAM, 1 side/1 layer) to 10.4 GB(MMVF, 2 sides/1 layer). Optical discs have made great strides inreplacing cassette tapes and floppy disks in the music and softwareindustries, and significant in-roads in replacing videocassette tapes inthe home video industry.

Data is stored on optical media by forming optical deformations or marksat discrete locations in one or more layers of the medium. Suchdeformations or marks effectuate changes in light reflectivity. To readthe data on an optical medium, an optical medium player or reader isused. An optical medium player or reader conventionally shines a smallspot of laser light, the “readout” spot, through the disc substrate ontothe data layer containing such optical deformations or marks as themedium or laser head rotates.

In conventional “read-only” type optical media (e.g., “CD-ROM”), data isgenerally stored as a series of “pits” embossed with a plane of “lands”.Microscopic pits formed in the surface of the plastic medium arearranged in tracks, conventionally spaced radially from the center hubin a spiral track originating at the medium center hub and ending towardthe medium's outer rim. The pitted side of the medium is coated with areflectance layer such as a thin layer of aluminum or gold. A lacquerlayer is typically coated thereon as a protective layer.

The intensity of the light reflected from a read-only medium's surfaceby an optical medium player or reader varies according to the presenceor absence of pits along the information track. When the readout spot isover the flat part of the track more light is reflected directly fromthe disc than when the readout spot is over a pit. A photodetector andother electronics inside the optical medium player translate the signalfrom the transition points between these pits and lands caused by thisvariation into the 1s and 1s of the digital code representing the storedinformation.

A number of types of optical media are available which permit anend-user to record data on the media, such optical media generally arecategorized as “writable” or “recordable,” or “rewritable.”

“Writable” or “recordable” optical media (e.g., “CD-R” discs) permit anend-user to write data permanently to the medium. Writable media aredesigned such that laser light in the writer apparatus causes permanentdeformations or changes in the optical reflectivity of discrete areas ofthe data layer(s) of the medium. Numerous writable optical media areknown, including those that employ a laser deformable layer in theirconstruct upon which optically-readable areas analogous to the pits andlands found in conventional read-only optical media can be formed (See,e.g., EP-A2-0353391), those that employ a liquid-crystalline material intheir data layer(s) such that irradiation with the laser beam causespermanent optical deformations in the data layer (See, e.g., U.S. Pat.No. 6,139,933 which employs such layer between two reflective layers toeffect a Fabry-Perot interferometer), and those that utilize a dye thatirreversibly changes state when exposed to a high power writing laserdiode and maintains such state when read with a low power reading laser(so-called, WORM, write-once-read-many times, optical media).

Rewritable optical media (e.g., “CD-RW”, “DVD-RAM”, “DVD−RW”, “DVD+RW”and “PD” media) use the laser beam to cause reversible opticaldeformations or marks in the data layer(s), such that the data layer iscapable of being written on, read, erased and rewritten on many times.Several rewritable optical media systems are known.

In one system, an optically-deformable data layer is deformed indiscrete areas by the writing laser to form optical changesrepresentative of the data, for example, pits and lands, and erased byuniformly deforming the same optically-deformable data layer, or theportion thereof wherein the data desired to be deleted is found. Inanother system, a photochromic material layer is used to store the data.In this system, the photochromic material reversibly changes when thematerial is irradiated by light possessing certain wavelengths. Forexample, a colorless compound may change its molecular state to aquasi-stable colored state when irradiated by ultraviolet (UV) light,yet be returned to the colorless state upon exposure to visible light.By selectively irradiating the photochromic material layer with the onewavelength to cause an optical change, and then irradiating with theother wavelength to reverse such optical change, one is permitted towrite, erase, and re-write data.

Materials that change color due to a change in crystalline state havebeen found to be particularly useful in rewritable media. In one system,a material that is dark in the amorphous state, but bright in thecrystalline state, is used to record the data. In such system, darkamorphous marks are formed utilizing a short high-power laser pulse thatmelts the recording material followed by quenching to temperatures belowthe crystalline temperature. The data formed thereby, can be erased byheating the amorphous state over a long enough period of time betweenthe temperature of crystallization and temperature of melt to regain thecrystalline state. Ternary stoichiometric compounds containing Ge, Sband Te (e.g., Ge₁Sb₂Te₄ Ge₂Sb₂Te₅) are in particular known to show alarge optical contrast between amorphous and crystalline phase and haveacceptable melting temperatures (t_(cryst)=about 150-200° C.,t_(melt)=about 600° C.). Alloys of such compounds with antimony (Sb),cadmium (Cd) and tin (Sn) have also been employed in rewritable media.

In rewritable optical media control information such as address data,rotation control signal, user information etc. is generally previouslyrecorded on the header field in the form of pre-pits.

Data may also be stored in what are referred to as fluorescentmultilayer disks. In fluorescent memory storage, the data is present aslocal variations of fluorescent substance properties. Typically thesubstance is illuminated with radiation at excitation wavelength, andthe fluorescence signal is registered at a different wavelength. Aspectral filter is used to separate the fluorescent signal at thereceiver from the noise of the excitation radiation. Data may be storedin a 3-D manner using the fluorescent principle. The two-photon approachis often utilized when the fluorescent medium is to be rewritable. Inthis approach a fluorescent medium containing photochromic moleculescapable of existing in two isomeric forms is used. The first isomericform is not fluorescent and has absorption bands for UV radiation, andis capable of being transferred into the second isomeric form upon thesimultaneous absorption of two long wavelength photons, said secondisomeric form being capable of exhibiting fluorescence.

Hybrid optical media are also known. For example, “half-and-half” discsare known wherein one portion of the disc has conventional CD-ROM pitsand the other portion of the disc has a groove pressed into the discwith a dye layer thereover to form a CD-R portion. A relatively newhybrid optical media is the CD-PROM (i.e., CD programmable ROM). TheCD-PROM medium combines a read-only CD-ROM format with a recordable CD-Rformat on one medium, but features only a single continuous groove onthe medium with the entire medium coated with a dye layer. The geometryof the continuous groove of the CD-PROM medium is modulated so as tolook like ROM pits to an optical reader. It also provides no dyetransition issues to overcome in manufacturing.

An optical disc medium read by moving a read head generating a radiationbeam in a specified path relative to the optical medium. The radiationbeam is used to differentiate regions having different opticalproperties, such different optical properties being used to representthe data, for example, the “on” logical state being represented by aparticular region. The detectable differences are converted intoelectrical signals, which are then converted to a format that can beconveniently manipulated by a signal processing system. For example, bysetting a threshold level of reflectance, transitions between pits andlands may be detected at the point where the signal generated from thereflectance crosses a threshold level. The pits represent a 1 and landsa 0. In this manner, binary information may be read from the medium.

The vast majority of commercially-available software, video, audio, andentertainment pieces available today are recorded in read-only opticalformat. One reason for this is that data replication onto read-onlyoptical formats is significantly cheaper than data replication ontowritable and rewritable optical formats. Another reason is thatread-only formats are less problematical from a reading reliabilitystandpoint. For example, some CD readers/players have trouble readingCD-R media, which has a lower reflectivity, and thus requires ahigher-powered reading laser, or one that is better “tuned” to aspecific wavelength.

Data is conventionally written onto pre-fabricated writable andrewritable medium individually, for example, one disc at a time, using alaser. Data is conventionally stamped onto read-only media by a diemolding (injection molding) process during the manufacture of theread-only medium. Today many more data-containing optical media can bemanufactured by the stamping process than by the laser writing processover a set unit of time, significantly reducing the cost of such stampedread-only optical media for large quantities of optical media. Themanufacturing of a stamped medium is also considerably cheaper than infabricating a fluorescent multi-layer medium.

Interference/reflectivity type optical media comprising a read-onlyformat are typically manufactured following a number of defined steps:

Data to be encoded on the medium is first pre-mastered (formatted) suchthat data can be converted into a series of laser bursts by a laser,which will be directed onto a glass master platter. The glass masterplatter is conventionally coated with a photoresist such that when thelaser beam from the LBR (laser beam recorder) hits the glass master, aportion of the photoresist coat is “burnt” or exposed. After beingexposed to the laser beam, it is cured and the photoresist in theunexposed area rinsed off. The resulting glass master is electroplatedwith a metal, typically Ag or Ni. The electroformed stamper medium thusformed has physical features representing the data. When large numbersof optical media of the disc-type are to be manufactured, theelectroformed stamper medium is conventionally called a “father disc.”The father disc is typically used to make a mirror image “mother disc,”which is used to make a plurality of “children discs” often referred toas “stampers” in the art. Stampers are used to make productionquantities of replica discs, each containing the data and trackinginformation that was recorded, on the glass master. If only a few discsare to be replicated (fewer than 10,000) and time or costs are to beconserved, the original “father” disc might be used as the stamper inthe mold rather than creating an entire “stamper family” consisting of“father,” “mother” and “children” stampers.

The stamper is typically used in conjunction with an injection molder toproduce replica media. Commercially-available injection molding machinessubject the mold to a large amount of pressure by piston-driven presses,in excess of 20,000 pounds.

In the optical medium molding process, a resin is forced in through asprue channel into a cavity within the optical tooling (mold) to formthe optical medium substrate. Today most optical discs are made ofoptical-grade polycarbonate which is kept dry and clean to protectagainst reaction with moisture or other contaminants which may introducebirefringence and other problems into the disc, and which is injectedinto the mold in a molten state at a controlled temperature. The formatof the grooves or pits is replicated in the substrate by the stamper asthe cavity is filled and compressed against the stamper. After the parthas sufficiently cooled, the optical tooling mold is opened and thesprue and product eject are brought forward for ejecting the formedoptical medium off of the stamper. The ejected substrate is handed outby a robot arm or gravity feed to the next station in the replicationline, with transport time and distance between stations giving thesubstrate a chance to cool and harden.

The next step after molding in the manufacture of a read-only format isto apply a layer of reflective metal to the data-bearing side of thesubstrate (the side with the pits and lands). This is generallyaccomplished by a sputtering process, where the plastic medium is placedin a vacuum chamber with a metal target, and electrons are shot at thetarget, bouncing individual molecules of the metal onto the medium,which attracts and holds them by static electricity. The sputteredmedium is then removed from the sputtering chamber and spin-coated witha polymer, typically a UV-curable lacquer, over the metal to protect themetal layer from wear and corrosion. Spin-coating occurs when thedispenser measures out a quantity of the polymer onto the medium in thespin-coating chamber and the medium is spun rapidly to disperse thepolymer evenly over its entire surface.

After spin-coating, the lacquer (when lacquer is used as the coat) iscured by exposing it to UV radiation from a lamp, and the media arevisually inspected for reflectivity using a photodiode to ensuresufficient metal was deposited on the substrate in a sufficiently thicklayer so as to permit every bit of data to be read accurately. Opticalmedia that fail the visual inspection are loaded onto a reject spindleand later discarded. Those that pass are generally taken to anotherstation for labeling or packaging. Some of the “passed” media may bespot-checked with other testing equipment for quality assurancepurposes.

Optical media have greatly reduced the manufacturing costs involved inselling content such as software, video and audio works, and games, dueto their small size and the relatively inexpensive amount of resourcesinvolved in their production. They have also unfortunately improved theeconomics of the pirate, and in some media, such as video and audio,have permitted significantly better pirated-copies to be sold to thegeneral public than permitted with other data storage media. Mediadistributors report the loss of billions of dollars of potential salesdue to high quality copies.

Typically, a pirate makes an optical master by extracting logic datafrom the optical medium, copying it onto a magnetic tape, and settingthe tape on a mastering apparatus. Pirates also sometimes use CD or DVDrecordable medium duplicator equipment to make copies of a distributedmedium, which duplicated copies can be sold directly or used aspre-masters for creating a new glass master for replication. Hundreds ofthousands of pirated optical media can be pressed from a single masterwith no degradation in the quality of the information stored on theoptical media. As consumer demand for optical media remains high, andbecause such medium is easily reproduced at a low cost, counterfeitinghas become prevalent.

A variety of copy protection techniques and devices have been proposedin the art to limit the unauthorized copying of optical media. Amongthese techniques are analog Colorstripe Protection System (CPS), CGMS,Content Scrambling System (CSS) and Digital Copy Protection System(DCPS). Analog CPS (also known as Macrovision) provides a method forprotecting videotapes as well as DVDs. The implementation of Analog CPS,however, may require the installation of circuitry in every player usedto read the media. Typically, when an optical medium or tape is“Macrovision Protected,” the electronic circuit sends a colorburstsignal to the composite video and s-video outputs of the playerresulting in imperfect copies. Unfortunately, the use of Macrovision mayalso adversely affect normal playback quality.

With CGMS the media may contain information dictating whether or not thecontents of the media can be copied. The device that is being used tocopy the media must be equipped to recognize the CGMS signal and alsomust respect the signal in order to prevent copying. The ContentScrambling System (CSS) provides an encryption technique to that isdesigned to prevent direct, bit-to-bit copying. Each player thatincorporates CSS is provided with one of four hundred keys that allowthe player to read the data on the media, but prevents the copying ofthe keys needed to decrypt the data. However, the CSS algorithm has beenbroken and has been disseminated over the Internet, allowingunscrupulous copyists to produce copies of encrypted optical media.

The Digital Copy Protection System (DCPS) provides a method wherebydevices that are capable of copying digital media may only copy mediumthat is marked as copyable. Thus, the optical medium itself may bedesignated as uncopyable. However, for the system to be useful, thecopying device must include the software that respects that “no copy”designation.

While presently available copy protection techniques make it moredifficult to copy data from optical media, such techniques have not beenshown to be very effective in preventing large -scale manufacture ofcounterfeit copies. The hardware changes necessary to effectuate manycopy protection schemes simply have not been widely accepted. Nor haveencryption code protection schemes been found to be fool proof in theirreduction of the copying data from optical medium, as data encryptiontechniques are routinely cracked.

There is a need therefore for a copy-protected optical medium, whichdoes not depend entirely on encryption codes, or special hardware toprevent the copying of the optical medium. Such optical media shouldalso be easily and economically manufactured given the currentstrictures of optical medium manufacture. The copy-protected mediashould also be readable by the large number of existing optical mediumreaders or players without requiring modifications to those devices.

DEFINITIONS

“Authentication Material” refers to a material used to authenticate,identify or protect an optical medium. The data recorded on an opticalmedium, for example, software, video or audio files, are notauthentication material.

“Communication System” refers to any system or network for transferringdigital data from a source to a target.

“Light-Changeable Material”: a material that absorbs, reflects, emits orotherwise alters electromagnetic radiation directed at the same. By“light-changeable compound” it is meant to include, without limitation,“light-sensitive”, “light-emissive” and “light-absorbing” compounds, asdefined below.

“Light-Emissive material”: a material that emits light in response toexcitation with light. Light emission can be a result ofphosphorescence, chemiluminescence, or fluorescence. By the term“light-emissive compounds,” it is meant to include compounds that haveone or more of the following properties: 1) they are a fluorescent,phosphorescent, or luminescent; 2) react, or interact, with componentsof the sample or the standard or both to yield at least one fluorescent,phosphorescent, or luminescent compound; or 3) react, or interact, withat least one fluorescent, phosphorescent, or luminescent compound toalter emission at the emission wavelength.

“Light-Absorbing Compounds”: compounds that absorb light in response toirradiation with light. Light absorption can be the result of anychemical reaction known to those of skill in the art.

“Light-Sensitive Material”: a material capable of being activated so asto change in a physically measurable manner, upon exposure to one ormore wavelengths of light.

“Non-Destructive Security Dye” refers to a security dye that does notrender media permanently unreadable.

“Opacity-Resistant Light-Sensitive Material”: a material capable ofbeing activated so as to change in a physically measurable manner, otherthan in opacity, upon exposure to one or more wavelengths of light. Anopacity-resistant light-sensitive material may be said to be reversiblewhen the activated change returns to the initial state due to thepassage of time or change in ambient conditions.

“Optical medium”: a medium of any geometric shape (not necessarilycircular) that is capable of storing digital data that may be read by anoptical reader.

“Recording Dye” refers to a chemical compound that may be used with anoptical recording medium to record digital data on the recording layer.

“Reader”: any device capable of detecting data that has been recorded onan optical medium. By the term “reader” it is meant to include, withoutlimitation, a player. Examples are CD and DVD readers.

“Read-only Optical Medium”: an optical medium that has digital datastored in a series of pits and lands.

“Recording Layer”: a section of an optical medium where the data isrecorded for reading, playing or uploading to a computer. Such data mayinclude software programs, software data, audio files and video files.

“Registration Mark”: a physical and/or optical mark used to allowprecise alignment between one substrate and another substrate such thatwhen the registration marks are aligned, the corresponding positions oneach substrate are known. For example, when two medium are juxtaposedagainst one another such that their registration marks are aligned, thepoint on one substrate corresponding to a physical and/or opticaldeformation on the other substrate is known.

“Re-read”: reading a portion of the data recorded on a medium after ithas been initially read.

“Reversible Light-Sensitive Material”: a light-sensitive material issaid to be reversible when the activated change returns to the initialstate due to the passage of time or change in ambient conditions.

“Security Dye” refers to a compound that may provide or alter a signalto protect the data on a storage medium.

“Temporary Material” refers to material that is detectable for a limitedamount of time or a limited number of readings.

SUMMARY OF THE INVENTION

The present invention provides an optical medium, and a method ofmanufacturer thereof, that provides copy protection by incorporating alight-changeable compound in or on the optical medium at discretepositions (loci) such that it provides for altering of the digital dataoutput from a section of the recording layer in a predictable manner.Such optical medium permits the data to be read without requiringalteration to the hardware, firmware or software used in optical mediareaders while preventing reproduction of the medium. The optical mediaof the present invention provide producers and distributors of digitaldata with a data distribution medium that prevents reproducing of theirdigital data, for example, software, audio and video. The presentinvention particularly relates to read-only optical medium including,but not limited to CD, CD-ROM, DVD, DVD-5, DVD-9, DVD-10, DVD-18 andDVD-ROM, where optical deformations representing the data are introducedpermanently into at least a portion of the optical medium prior todistribution to an end-user. As would be understood by one of ordinaryskill in the art, however, the present invention may also be used withwritable and rewritable optical media such as CD-R and DVD-R.

The present inventors have discovered a method for altering and/oraugmenting the optically-read data stored on an optical medium in amanner that does not prevent the underlying data from being read by aconventional optical medium reader, but prevents the production of auseable optical medium copy using such conventional optical mediumreaders. The present inventors have found that by selectively placingcertain reversible light-changeable materials, and in particularlight-emissive materials, at discrete positions on an optical medium,that a conventional optical reader can be made at the first pass of suchpositions to read the data represented by the optical deformationscorrectly, but on a second pass read the data differently due to theactivation of the reversible light-changeable material. That is, thepassing light of the reader may be used to influence the compound andchange its properties so that upon re-reading, the data signal that isreceived by the detector is different from that which was received uponinitial sampling. For example, the light-changeable compound may becomereflective within a timeframe that provides for reflectance of the lightbeam upon resampling. Alternatively, the light-changeable material mayprovide for delayed emission or absorbance of light, thereby alteringthe signal either positively or negatively.

As most optical media readers and players are pre-programmed tore-sample data areas of the recording layer to assure correct copying,optical medium of an embodiment of the present invention will fail tocopy, as a data string read from the recording layer will vary accordingto whether the light-changeable material is activated upon sampling.That is, re-sampling of a data area in proximity to the light-changeablematerial may result in a different data read than when the data wasinitially read. Even if a copy can be made, that copy will be invalid ifa program on the optical medium requires two different reads to accessdata on the optical medium. That is, the copy will be invalid since itwill only represent one of two possible states at that data locus.

The present invention provides for specific optical media designs, andmethods for manufacturing such designs, that incorporatelight-changeable materials in a manner that selectively changes the dataread-out of the recording layer of an optical medium upon re-sampling ofthose portions of the recording layer in proximity to thelight-changeable material foci. In particular, there is provided opticalmedium designs that may be easily and economically produced withoutsignificantly altering the injection molding manufacturing process ofread-only optical media (as set forth above).

In a first embodiment of the present invention there is provided anoptical medium having light-changeable material selectively imprinted orplaced on the non-impressed (i.e., non-stamped) side of the recordinglayer of an optical medium. Such medium comprises a first substratehaving two major surfaces, a data track disposed along one major surfaceof the first substrate, and a light-changeable compound disposed on theother major surface of the first substrate cooperating with the datatrack to alter the data upon excitation with a suitable light stimulus(e.g., a particular wavelength). Such optical medium further preferablycomprises a second substrate, preferably of similar optical properties(preferably of the same material), affixedly attached to the surface ofthe substrate where the light-changeable compound is disposed.

A first embodiment optical medium of the present invention may beproduced by disposing the light-changeable material onto thenon-impressed side of the substrate after the substrate has been stampedand sufficiently cooled, and after the optical tooling mold is opened(but before the sprue and product eject are brought forward for ejectingthe formed optical medium off of the stamper). As would be understood byone of ordinary skill in the art such manufacturing technique permitsprecise registration of the light-changeable material with the dataimpressions on the other surface of the substrate. Preferably thelight-changeable material is covered by a second substrate of similar(or identical) optical properties to protect the light-changeablematerial from its ambient environment. Such second substrate may beaffixed to the first substrate either before or after the sputteringstep used to cover the stamped surface of the first substrate. Either orboth of the first and second substrates may be spin-coated with anadhesive agent prior to formation of such optical medium such that thelayers may be affixedly attached. Alternatively, the light-changeablematerial may be coated with a polymer, as by spin-coating. For example,an optically-pure lacquer may be used to coat the light-changeablematerials.

In a second embodiment of the present invention, there is provided anoptical medium comprising a first substrate layer having a first majorsurface and a second major surface, said first major surface of saidfirst substrate layer having light-changeable material thereon, andeither of said first or second major surface of said first substratelayer, or both, having a registration mark thereon; a second substratelayer having a first major surface and a second major surface, saidfirst major surface of said second substrate layer having informationpits thereon, and either of said first or second major surface of saidsecond substrate, or both, having a registration mark thereon, saidsecond major surface of said second substrate being disposed along saidfirst major surface of said first substrate layer such that theregistration marks of said first and second substrates are aligned; ametal reflector layer, said metal reflector layer being disposed alongsaid first major surface of said second substrate layer; a firstovercoat layer being disposed along said metal reflector layer, andoptionally a second overcoat layer being disposed along said secondmajor surface of said first substrate layer.

A second embodiment optical medium may be produced by obtaining a firstsubstrate having a first major surface and a second major surface and aregistration mark on either of said first or second major surface, orboth; imprinting in discrete positions on said first major surface ofsaid first substrate layer light-changeable material; obtaining a secondsubstrate having a first major surface and a second major surface, and aregistration mark on either of said first or second major surface, orboth, said first major surface of said second substrate layer havinginformation pits thereon; disposing said second major surface of saidsecond substrate along said first major surface of said first substratesuch that the registration marks on said first and second substrate arealigned and affixing said second major surface of said second substrateto said first major surface of said first substrate; metalizing saidfirst major surface of said second substrate layer having saidinformation pits; disposing a first overcoat layer along said metalizedsurface; and optionally disposing a second overcoat layer along saidsecond major surface of said first substrate layer. As would beunderstood by one of ordinary skill in the art, the registration marksneed not be on the actual surface of a substrate, but need to bedetectable. By “a surface having a detectable registration mark” it ismeant that a registration mark is detectable therethrough or thereon.

In a third embodiment of the present invention, there is provided anoptical medium comprising a substrate having material(s) capable ofreacting with one another, or being activated, such that they form alight-changeable material(s) upon exposure to a particular light sourceof defined energy, such material being coated on the non-impressed(i.e., non-stamped) side of the recording layer of an optical medium.Such optical medium comprises a first substrate, a data track disposedalong one surface of the first substrate, and the material(s) capable ofbeing activated to form a light-changeable material(s) upon exposure toa particular light source (of defined energy) coated on the non-embossedsurface of the first substrate. For example, a laser may catalyzecrosslinking of certain inactive material(s) to form light-changeablecompounds, such as a light-emissive material. In this embodiment, thecoated material is activated in discrete areas using the appropriatelight source (and energy) so as to form a light-changeable material atdiscrete points which will cooperate by their positioning with respectto the data track to alter the data upon excitation with a suitablelight stimulus (e.g., a particular wavelength). This selectiveactivation of various portions of the first substrate to form alight-changeable compound may be performed in a manner similar to thatused to write data to a CD-R disc. Such optical medium furtherpreferably comprises a second substrate, preferably of similar opticalproperties (preferably of the same material), affixedly attached tosurface of the substrate where the formed light-changeable compounds aredisposed. In an alternative to such embodiment, the material coated onthe non-embossed (i.e., non-stamped) side of the recording layer of anoptical medium may be light-changeable material that may be selectivelydeactivated using a laser of particular wavelength and strength. In suchcase selective activation in the appropriate data spots can be caused bydeactivating those portions of the coat which one does not wish to havelight-changeable properties.

In a fourth embodiment of the present invention there is provided anoptical medium comprising a substrate having two major surfaces, onemajor surface of the substrate having a data track disposed thereon, anda cohesive layer disposed above such data track, the cohesive layercontaining light-changeable material cooperating with data track so asto alter the read of the data stored therein upon excitation with asuitable light stimulus (i.e., activation of the light-changeablematerial). A preferred optical medium of such embodiment comprises afirst molded layer having a data track disposed thereon, a firstpolymeric layer covering the data track, second polymeric layercomprising the light-changeable material, and a third polymeric layercovering the second polymeric layer. The first polymeric layer maycomprise a dielectric layer. The first and second polymeric layers arepreferably less than 3 nm in thickness.

In a fifth embodiment, there is provided copy protection in that theoptical medium itself has code that instructs the optical reader tore-sample a data area where a light-changeable material is found (orwhere the light-changeable material affects the read), and to fail topermit the access to the data if upon re-reading the data area, thatdata elicited is the same as upon initial sampling. In anotherembodiment, the light-changeable compound must be located at aparticular locus for the optical media in operate. For example, softwaremay be included on the optical medium to direct the optical reader toalter its focal length such that the light-changeable material in aplane different from the optical data is detected and access to theoptical data permitted only if such light-changeable material isdetected.

Yet in a sixth embodiment of the present invention, an optical mediumhaving light-changeable material is formed by selectively placing thelight-changeable material into a pit or onto a land of a standardoptical medium using microinjection techniques, well known in the art,prior to the metalizing step.

And yet in a seventh embodiment of the present invention, an opticalmedium having a adhesive material comprising the light-changeablematerial, said adhesive material being adhered to one or more layer orsurfaces of the medium is disclosed. For example, light-changeablematerial may be placed in a label, or in an optically clear material ona layer or surface of the medium such that the light-changeable materialis positioned in the manner desired.

And yet in an eighth embodiment of the present invention there isprovided an optical medium comprising a substrate having two majorsurfaces, a first major surface having a data track disposed thereon, areflective layer disposed along the data track, and a layer containinglight-changeable material disposed over the reflective layer. The datatrack may comprise a plurality of impressions on the optical medium. Thereflective layer may be formed by sputtering of reflective material ontothe data track. It is preferred in such embodiment that the reflectivelayer has one or more holes or punctuate discontinuities therein thatpermit light which passes through the first major surface to passtherethrough and to impinge on a portion of the light-changeablematerial layer. The punctuate discontinuities may be formed by anymethod known in the art, for example by means of a high-powered laser.The light-changeable material may be embedded in the lacquer currentlyused to seal the optical medium Alternatively, the UV-cured lacquercurrently in use may cover the light changeable material. Removal ofportions of the reflective layer would allow the reading laser of aconventional optical reader to impinge upon the light-changeablematerial layer at sites where the reflective layer was removed.

As would be understood by one of ordinary skill in the art, thepunctuate discontinuities of such embodiment may be formed in thereflective layer in a planned manner such that on the first read-passpits and lands (whether correlated with a punctuate discontinuity ornot) are read in a conventional manner, but on a subsequent read a pitand/or land associated with a discontinuity in the reflective layer isnot read conventionally. For example, a pit associated with adiscontinuity in the reflective layer may be read as a pit on the firstread, but on subsequent read as a land due to a change in thelight-changeable material layer which is detected (due to thediscontinuity in the reflective layer) by the reading laser as a changein physical structure of the data track (such as when thelight-changeable material emits sufficient light to increase the lightreceived by the reading laser to be above threshold on a subsequentread). A subsequent read may be effectuated by either software orfirmware.

While not limited to any particular manufacturing process, opticalmedium of such embodiment may be manufactured by modification ofconventional optical disc manufacture techniques. The medium may beinjected molded and metalized as discussed above with respect to themanufacture of conventional read-only optical discs. The disc may thenbe placed into a glass mastering device or modified CD writer, andselect areas of the metalized layer removed to form punctuatediscontinuities in the layer. The light-changeable material layer maythen be placed, as for example by spin coating, on the non-reading sideof the medium such that the light-changeable material layer in a mannersuch the same would be accessible to the reading laser only through thepunctuate discontinuities in the metalized layer. As would be understoodby one of ordinary skill in the art, formation of the punctuatediscontinuities is preferably performed in a manner such that neitherthe first read nor any subsequent read after activation of thelight-changeable material results in rejection of the data read due toany standard error protocols employed with respect to the medium, suchas CIRC and/or EFM.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute partof the specification, illustrate presently preferred embodiments of theinvention, and together with the general description given above and thedetailed description of the preferred embodiments given below, serve toexplain the principles of the invention.

FIG. 1 is a cross-sectional view of a conventional prior art opticalstorage medium of the type generally referred to as a read-only opticalstorage disc;

FIG. 2 is a cross-sectional view of an exemplary optical storage mediumof the present invention;

FIG. 3 is a cross-sectional view of an another exemplary optical storagemedium of the present invention;

FIG. 4 is a cross sectional view of an optical storage medium whereinthe photosensitive material is located in a layer separate from thecontent data;

FIG. 5 is a diagrammatic flow chart of a conventional prior artinjection molding technique for manufacturing read-only optical media;

FIG. 6 is a diagrammatic flow chart of a preferred method of the presentinvention for manufacturing read-only optical media with minormodification to the conventional injection molding for manufacturingread-only optical media of the type set forth in FIG. 2.

FIG. 7 is a diagrammatic flow chart of a preferred method of the presentinvention for manufacturing read-only optical media with minormodification to the conventional injection molding for manufacturingread-only optical media of the type set forth in FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

The present invention overcomes many of the problems associated withprior art optical media copy-protection systems. The present inventionprovides optical media that use certain innate physical properties ofthe optical medium composition to prevent efficient copying of theoptical medium. The invention provides for the altering of digital dataoutput during the reading of such optical media in such a manner thatdata is allowed to be read while preventing reproduction of the media.Such invention does not require alterations to the hardware, firmware orsoftware used in conventional optical readers. The alteration ofdata-reads is accomplished by selectively placing light-changeablecompounds in the media, such light-changeable compounds preferablyreacting upon excitation from the light used by a conventional opticalreader. By selective placement of such light-changeable materials, aconventional optical reader may read optically encoded data one wayprior to activation of the light-changeable material, and in anothermanner after activation, and yet in the first manner when thelight-changeable materials are no longer activated.

As would be understood by one of ordinary skill in the art, a transitionfrom a land to a pit, or pit to a land, is conventionally interpreted bya standard optical reader as a “1”. However, if a pit is in the midst ofother pits, or a land is in the midst of other lands, a “0” will beregistered. By selectively placing light-sensitive material with respectto the pits and lands, one can affect the read of the data. For example,given a land of length 3T immediately preceding a pit of length 6T thatis followed by a land of 3T, a conventional optical disc reader wouldread a data stream of 00100000100, where each transition from a pit to aland is read as a “1”. If a light changeable material is readable by areader over a 3T length of the 6T pit upon a subsequent read, the datastream may be read instead as 00000100100. That is, the transitions canbe moved by causing the reader to detect a transition from a pit toland, or vice versa, wherein no physical transition actually exists.

The light-changeable material may be selectively placed in register withthe data pits and lands and the checksums set on the optical medium takeinto account the changeable data strings such that the Cross-InterleaveReed-Solomon Code (“CIRC”) decoder (standard on all CD players/readers)does not detect a read error preventing the underlying data from beingread. Up to three percent of demodulated incoming frames from thereading laser can be corrected by an enhanced CIRC decoder. Both thedata represented by the pits and lands, and the data represented by thelight-changeable material may need to be decoded to correct data stringsby the CIRC decoder. Alternatively, the light-changeable material may beplaced in a separate layer planar to the injection molded data withoutregard to registry.

When the two different data sets readable from the locus are used tocause proper read of the optical medium (e.g., when a softwareinstruction set on the optical medium or elsewhere requires twodifferent data reads at a locus for proper functioning), it may bepreferred that the light-changeable materials employed exhibit long termstability under typical optical media storage conditions and that thelight-changeable materials be light fast and non-reactive permitting theoptical medium to be used over a long period of time. On the other hand,it may be preferred in some applications that the chosenlight-changeable material degrade over a period of time such that theoptical medium can be read only over a limited time period as, forexample, with demonstration discs.

Demonstration discs are often provided to consumers to entice them intobuying a full-fledged release of the product. Demonstration discs areoften packaged to provide limited functionality (i.e., not allowing allaspects of the fully functioning software to be executed) and/or containinstruction sets that limit the number of times that the disc can beemployed by the user. The present invention provides advantage over suchdemonstration discs in that a demonstration disc employing teachings ofthe present application could be made to be fully functional, and yetdesigned to lack functionality after a period of time or after a numberof uses, without need to resort to purely (possibly hackable) softwaremeans to effectuate the same.

Light-changeable compounds may be chosen from any compound orcombination of compounds that serve to change the output signal from themedium upon re-reading. These compounds include, without limitation,delayed emission compounds, delayed absorbance compounds and otherlight-changeable compounds. A layer in the medium that becomesreflective upon re-reading may also be useful in predictably alteringthe output of the medium.

The light-changeable compounds of the present invention may be eitherorganic or inorganic in nature, a combination of both, or mixturesthereof. The compounds preferably demonstrate delayed response to thewavelength(s) of light to which they are sensitive, such that the datacan be read by the reader in at least a first intended form upon initialread, and upon re-sampling in at least a second intended form.

In a preferred embodiment the light-changeable compounds are compoundscapable of light-emission upon stimulation with one or more wavelengthsof light. Preferably the light-emissive light-changeable compounds emitat wavelengths that are in the same, or about the same, as thewavelengths that are detected by the readers. For example, with a CD itis preferred that the light-changeable compound emit at a wavelength ofabout 780 nm and with a DVD that the light-changeable compound emit at awavelength of about 650 nm.

As stated above, the light-changeable compounds may be organic innature, as for example, a dye. A particularly useful class of organicdyes of the present invention is the cyanine dyes. These cyanine dyesinclude, among others, indodicarbocyanines (INCY),benzindodicarbocyanines (BINCY), and hybrids that include both an INCYand a BINCY. Hybrids may be, for example, mixtures of two different dyesor, in another embodiment, compounds that include both INCY and BINCYmoieties. In one embodiment, the light-changeable compound is aratiometric compound having a linked structure with excitation ranges atboth the CD and DVD ranges of about 530 and 780 nm. In a furtherembodiment, the dye is phosphorescent, having a time delay of about 10milliseconds.

Table 1 provides some organic dyes that may be useful with theinvention.

TABLE 1 Dye Name/No. CD/DVD Excitation Emission Alcian Blue DVD 630 nmAbsorbs (Dye 73) Methyl Green DVD 630 nm Absorbs (Dye 79) Methylene BlueDVD 661 nm Absorbs (Dye 78) Indocyanine Green CD 775 nm 818 nm (Dye 77)Copper Phthalocyanine CD 795 nm Absorbs (Dye 75) IR 140 CD 823 nm (66ps) 838 nm (Dye 53) IR 768 Perchlorate CD 760 nm 786 nm (Dye 54) IR 780Iodide CD 780 nm 804 nm (Dye 55) IR 780 Perchlorate CD 780 nm 804 nm(Dye 56) IR 786 Iodide CD 775 nm 797 nm (Dye 57) IR 768 Perchlorate CD770 nm 796 nm (Dye 58) IR 792 Perchlorate CD 792 nm 822 nm (Dye 59)1,1′-DIOCTADECYL-3,3,3′,3′-TETRAMETHYLINDODI- DVD 645 nm 665 nmCARBOCYANINE IODIDE (Dye 231) 1,1′-DIOCTADECYL-3,3,3′,3′-TETRAMETHYLINDODVD 748 nm 780 nm TRICARBOCYANINE IODIDE (Dye 232)1,1′,3,3,3′,3′-HEXAMETHYL-INDODICARBOCYANINE DVD 638 nm 658 nm IODIDE(Dye 233) DTP CD 800 nm (33 ps) 848 nm (Dye 239) HITC Iodide CD 742 nm(1.2 ns) 774 nm (Dye 240) IR P302 CD 740 nm 781 nm (Dye 242) DTTC IodideCD 755 nm 788 nm (Dye 245) DOTC Iodide DVD 690 nm 718 nm (Dye 246)IR-125 CD 790 nm 813 nm (Dye 247) IR-144 CD 750 nm 834 nm (Dye 248)

As also stated above, the light-changeable compounds may also beinorganic in nature. Inorganic compounds find particular use in thepresent invention when the light-changeable material is desired to befunctional for long periods of time on the optical medium. Inorganiccompounds are less prone to degrade when exposed to repeated laserchallenges.

Inorganic compounds capable of light-emission may find use in thepresent invention. Compounds such as zinc sulfide (ZnS) at variousconcentrations (Seto, D. et al., Anal. Biochem. 189, 51-53 (1990)), andrare earth sulfides and oxysulfides, such as, but not limited to,ZnS—SiO₂, Zn₂SiO₄, and La₂O₂S are known to be capable of emittingphosphorescence at certain wavelengths. Such inorganic light-emissivecompounds may be used advantageously with a metal ion such as manganese(Mn), copper (Cu), europium (Eu), samarium (Sm), SmF₃, terbium (Tb),TbF₃, thulium (Tm), aluminum (Al), silver (Ag), and magnesium (Mg).Phosphorescent and luminescent properties of the compounds can bealtered in a ZnS crystal lattice, for example, the delay time andwavelength of emission be controlled by changing the metal ions used forbinding (See, e.g., U.S. Pat. No. 5,194,290).

Inorganic phase change materials can also be used to effectuate thepresent copy protection invention. Particularly useful inorganic phagechange materials include chalcogenide materials such as GeSbTe, InSbTe,InSe, AsTeGe, TeO_(x)—GeSn, TeSeSn, SbSeBi, BiSeGe and AgInSbTe-typematerials which can be changed from an amorphous state to a crystallinestate by absorption of energy from particular light sources. The phasechange should be timed such that the data underlying the phage changematerial can be read before the change occurs. The phase change shouldalso be persistent enough that upon re-sampling a different data read isobtained, and yet not too persistent such that the underlying data isobfuscated for significant periods of time. Software on the opticalmedium should be keyed to the period of time involved in the change ofphase and return to original phase. In a preferred embodiment thetransition from amorphous to crystalline state should not last moreencompass more than about 300 msec. Multiple reads in the same spot canbe used to induce a temperature change, as can laser pumping, causingphase change activation at a specific point or locus.

The inorganic compound(s) may be used in numerous forms as would beunderstood by one of ordinary skill in the art, including, withoutlimitation, in very fine particle size, as dispersions or packed withina crystal lattice (See, e.g., Draper, D. E., Biophys. Chem. 21: 91-101(1985)).

Given that the pit size on a typical CD ROM is 0.8 μm, and on a typicalDVD 0.4 μm, it is preferred that the inorganic or organiclight-changeable materials used in the present invention be smaller thanthe respective pit sizes.

In conventional “read only” type optical media, the light-changeablematerial may be placed at the pit and/or land level, or in registertherewith, such that, for example with respect to a delayedlight-emissive material, a pit may be read as a land when re-sampling ofthe data occurs and the light-changeable material emits light. Inwritable or recordable optical media the light-changeable material ispreferably placed in the phase change layer in a manner to interferewith the read of the substrate change in the manner such change isotherwise intended to be read.

Numerous methods may be used to allow for the precise placement of thelight-changeable material with respect to the data structure (i.e., thepit, land, deformation, etc. read as data) that is desired to beobscured upon activation of the light-changeable material. For example,the light-changeable material may be formulated with an uv cure resin orother photoinitiator which is able to effectuate a cure in thewavelengths associated with readers (400-800 nm) or in the UVA, UVB andUVC range (254 nm-365 nm) and placed as a layer over the optical medium.A laser beam of appropriate wavelength may be used to cure the resin ata precise point on the optical medium and the remaining uv cure resinwashed off. A photomask may be used to pin point the cure on the opticalmedium. In such a technique, the light-changeable material is placed ina light sensitive film, which is laid on the optical medium. Thephotomask is used to allow directed cure of the film by permittingcuring light to pass through the photomask at certain positions therebyplacing the light-changeable material in the desired positions on theoptical medium. Alternatively, quantum dots or nanocrystals (Peng et al.J. Am. Chem. Soc. 119: 7019 7029 (1997), or fluorescent microspheres(such as Fluospheres available form Molecular probes, Oregon, USA) canbe used for precise placement on the optical medium. Suchmicro-materials may be placed in discrete positions by, for example,using lithographic process such as photomasking. As Fluosphere beads canbe made from 0.2 μm-4.0 μm in size, such spheres may be placed at thepit level.

Instead of direct registration of the light-changeable material with apit, land or other data structure, that is the content data, thelight-changeable material may be placed in a separate layer planar tothe injection molded data without regard to registry.

The light-changeable material may also be placed on the optical mediumin a bound spin-coat rather than specifically placed in discrete pointsor localities. Preferably, in such case, the spin-coat is uniform inthickness. The thickness of the light-changeable material layer in suchembodiment may be controlled by varying, among other factors, therotational speed of the media during the spin coat process. Thethickness of the layer will vary according to the application, but isgenerally between about 160 nm to less than 1 nm thick. The desiredthickness of the layer comprising the light-changeable material may varyaccording to the absorption of the material, the emission of thematerial, the density of the material and the structure of the media, aswell as the properties of the reader that is used to read the data offof the media. It is typically preferred that the light-changeablematerial layer be applied at a thickness that is thin enough to allowtransmission of light to adequately read the underlying data uponinitial sampling, while being dense enough to provide adequate change,such as light emission, upon oversampling with the same reader. For manyapplications a film thickness of from 50 to 160 nm is found useful. Formost CDs the film thickness is in the range of from about 70 nm to about130 nm, while for most DVD the film thickness is preferably in the rangeof from about 50 nm to about 160 nm.

As would be understood by one of ordinary skill in the art, thepersistence of the activated state of the light-changeable material,such as a light-sensitive material, (i.e., the length of time thematerial is in the activated state versus initial state) and the delayin the conversion of the initial state to the activated state (i.e., thelength of time it takes the material to enter the activated state fromthe initial state) are important to permit the proper read of theunderlying data, and for causing a change in the data read uponre-sampling. Given a pit size of 8 μm, and a typical rotational speed of1.2 m/sec in a CD-ROM, the preferred delay in a CD is a minimum of about6.85×10⁻⁷ seconds. Given a pit size of 0.4 μm, and a rotational speed ofabout 3.5 m/sec in a DVD, the preferred delay in a DVD is a minimum ofabout 1.14×10⁻⁷. If the delay is too quick the data below thelight-changeable material will be obscured prior to read.

The rotational speed, that is the time it takes for a reader to get backto the same area on the optical medium, differs for conventional CDs andDVDs. The persistence of the activated state should at least last thislong. Given a 120 mm diameter and a rotational speed of about 1.2 m/sec,the light-changeable material placed on a CD should display apersistence of at least about 300 msec. Given a 120 mm diameter, and arotational speed of about 3.5 m/sec, the light-changeable materialplaced on a conventional DVD should display a persistence of at leastabout 100 msec. If the persistence is too short, the activated statewill not be seen to obscure the underlying data upon re-sampling. Ofcourse, if persistence is too long it may not allow the data on theoptical medium to be read in an acceptable time after activation of thelight-changeable material. Persistence of certain inorganiclight-changeable materials, such as zinc sulfide, can be controlled byaltering the particle size, or by inserting certain metals or ions in alattice of zinc sulfide (ZnS) or a crystal lattice of ZnS—SiO₂, forexample persistence of fluorescence of ZnS can be altered by doping itwith different metals or ions such as Eu, Sm Tb, Cu, Mn, Al, and Mg atvarious concentrations.

It is generally preferred that the particle size be less than 100 nm,more preferably less than 10 nm, and no more than the pit size of theoptical medium being read (about 0.8 μm for the conventional CD, andabout 0.4 μm for the conventional DVD). The light-changeable materialshould be placed on the optical medium in a manner that the coating isnot so thick as to cause scatter and incoherence. Preferably, anycoating of the light-changeable material should be less than 100 nm.When the light-changeable material changes reflectivity upon activation,the minimum change in the index of refraction on a pit/land basedoptical medium should be at least about 0.3 to 0.4 to correspond to thechange in index of refraction between a pit and a land.

The present invention may be used with conventional optical media suchas CDs and DVDs. The invention may also be incorporated into massproduction techniques that are currently used to produce “read-only” CDsand DVDs, and hybrid read-only/recordable or rewritable data forms, andother physical optical medium formats, with minimal changes in theproduction equipment and line. As would be understood by one of ordinaryskill in the art, the present invention may also be employed withrecordable or rewritable data forms, albeit, more changes in theproduction equipment may be required.

Now turning to the figures, there is shown in FIG. 1 a cross-sectionalview of a prior art read-only optical storage medium 10 for storingpre-recorded data in a manner that can be read by a radiation beaminteracting with the medium. A transparent polycarbonate substrate layer12, or similar material having an optical transmission characteristicwhich permits the radiation interacting with the recording layer to betransmitted therethrough. An aluminum reflector layer 14 is foundadjacent to polycarbonate substrate layer 12. Polycarbonate layer 12 isfabricated with the data stored as surface structure, illustrated aslands 16 and pits 18. Aluminum reflector layer 14 is disposed in such amanner as to provide a surface generally retaining the structure of thepolycarbonate surface. A protective overcoat layer 20 is applied toaluminum reflector layer 14 in an uncured state and is cured byultraviolet radiation. Also shown in FIG. 1 are the laser beaminteraction with a position on a pit (51), and the laser beaminteraction at a land (53).

FIG. 5 is a diagrammatic flow chart of a conventional prior artinjection molding technique for manufacturing read-only optical media.Manufacture of an optical medium begins with premastering 22(formatting) of the data. The premastered data is used to control alaser used in the glass mastering step 24 to remove photoresist materialfrom a photoresist coated glass plate. The photoresist material is burntby the laser, the photoresist is cured and unexposed photoresist rinsedoff, and the resulting data-bearing glass master is then electroformedwith a metal such as Ag or Ni (step 26) to form a father, in the case ofa disc, known as the “father disc.” The father disc may be used as atemplate to make a mirror image disc, known in the art as the motherdisc (step 28). Mother disc is used to make optical duplicates of thefather disc (step 30), such discs being referred to as children discs.Children discs are referred to as stampers when used to produce multiplediscs in an injection molder. If an entire disc “family” is not created,the father disc may be used directly as the stamper.

The injection molding step 32 uses a stamper to form deformations in themanufactured discs representative of the premastered data ofpremastering step 22. The manufactured optical media are then removedfrom the mold and allowed a cool down period, known in the art as thebuffering step 34. The surface of the polycarbonate substrate carryingthe deformations is coated with metal in metal sputtering step 36. Inmetal sputtering step 36 metal is coated over and within thedeformations to form a metal layer over the polycarbonate substrate.Both the metal layer and the non-metalized polycarbonate substratesurfaces are coated with a protective polymer, typically lacquer, inspincoat step 38. The spincoated layers are then cured at UV curing step40. The optical media are then inspected at visual inspection step 42and the optical media are approved or rejected.

FIG. 6 is a diagrammatic flow chart of a preferred method of the presentinvention for manufacturing read-only optical media with minormodification to the conventional injection molding for manufacturingread-only optical discs of the type set forth in FIG. 2. As seen in theflow chart, additional steps 46 and 48 are added to the conventionalmethod set forth in FIG. 5. Light-changeable material is imprinted atstep 46 on the surface of the mold which is not impressed with the childdisc (i.e., the stamper) while the stamper is still in contact with themolding material, after the molding material has sufficiently cooled soas not to damage the light-changeable properties of the material, andbefore the molded substrate is removed from the molding apparatus.Imprinting may be done, for example, using gravure, laser printing,Mylar screen-printing, drop-on-demand printing, CU or other methodsknown in the art for imprinting materials. The resulting optical mediumis treated as set forth above in FIG. 5, with the additional step 48 ofadding a second polycarbonate substrate or protective layer over thesurface imprinted with the light-changeable material to protect suchmaterial for the ambient environment. FIG. 2 is a cross-sectional viewof an exemplary optical storage medium manufactured by such techniquecomprising spin coat layers 50, metalized layer 52, impressedpolycarbonate layer 54, light-changeable material 56, bonding materiallayer 58, second polycarbonate layer 60.

Now turning to FIG. 7 is a diagrammatic flow chart of a preferred methodof the present invention for manufacturing read-only optical medium withminor modification to the conventional injection molding formanufacturing read-only optical media of the type set forth in FIG. 3.The flow chart of FIG. 7 differs from that of the conventional techniquefor manufacturing read-only optical media of FIG. 5, in including step62 wherein light-changeable material is printed onto a secondpolycarbonate material. As would be apparent to one of ordinary skill inthe art, step 62 can be concurrent with, prior to, or after theinjection molding of the first substrate. Second polycarbonate substrateis affixed to the metalized polycarbonate medium having the informationpits at step 64, which also may be performed other stages in thetechnique as would be understood by one of ordinary skill in the art.For example, the first substrate may be metal sputtered at the same timethat the light-changeable material is being imprinted on the secondsubstrate. Attachment of the second polycarbonate substrate may be meansof a hot melt or by way of bonding materials. FIG. 3 is across-sectional view of an exemplary optical storage medium manufacturedby such technique comprising spin coat layers 50, metalized layer 52,impressed polycarbonate layer 54, light-changeable material 56, bondingmaterial layer 58, second polycarbonate layer 60.

FIG. 4 a cross sectional view of yet another optical storage medium ofthe present invention wherein the photosensitive material is located ina layer 66 separate from the content data. The photosensitive materialmay be printed on layer 66 by, for example, an ink jet printer. Theoptical medium of FIG. 4 may be produced after UV curing step 40 of FIG.5 in that the light-sensitive material layer 66 may be placed on top ofthe spin coated lacquer layer 68, that sits atop of the data bearinginjection molded layer 70. Another spin-coated lacquer layer 72 is shownin the figure to overlie layer 66, to protect such against damage.

While the invention has been described with respect to preferredembodiments, those skilled in the art will readily appreciate thatvarious changes and/or modifications can be made to the inventionwithout departing from the spirit or scope of the invention as definedby the appended claims. All documents cited herein are incorporated intheir entirety herein.

1. A computer-readable medium having material at a select positiontherein/thereon and containing instructions for controlling an opticalreader to cause the optical reader to re-read the position having thematerial one or more times to elicit a measurable parameter at such aposition.
 2. The computer-readable medium of claim 1 wherein thematerial is a light-changeable material.
 3. The computer-readable mediumof claim 2 wherein the measurable parameter is a light change.